Metal materials suitable for organic coating

ABSTRACT

METAL MATERIALS RECEPTIVE TO ORGANIC COATINGS AND HAVING A FILM COMPOSED MAINLY OF HYDRATED CHROMIUM OXIDE ON THE SURFACE OF METAL OR PLATED METAL AND A LAYER OF WATER SOLUBLE VEHICLE CONTAINING AT LEAST ONE SELECTED FROM THE GROUP CONSISTING OF OLEORESINOUS RESINS, ALKYD RESINS, AMINOALKYD RESINS, PHENOLALKYD RESINS AND ACRYLIC, RESINS ON THE HYDRATED CHROMIUM OXIDE FILM.

United States Patent() Inf. ci. Bszb /04 U.S. Cl. 29-195 12 Claims ABSTRACT OF THE DISCLOSURE Metal materials receptive to organic coatings and having a film composed mainly of hydrated chromium oxide on the surface of metal or plated metal and a layer of Water soluble vehicle containing at least one selected from the group consisting of oleoresinous resins, alkyd resins, aminoalkyd resins, phenolalkyd resins and acrylic, resins on the hydrated chromium oxide film.

This invention relates to metal articles, such as metal sheets, which are surface-coated with a chromiumcontaining layer or film, wherein the chromium-containing layer or film is in turn coated with a protective film or adsorbed layer of a water-soluble vehicle. The chromium-containing layer or film comprises as major component hydrated chromium oxide and is formed by chromic acid treatment of the metallic substratum proper or of a plated surface of the metallic substratum. The protective film or adsorbed layer of the Water-soluble vehicle is in turn formed by treating the chromium-containing layer or film with an aqueous solution of the water-soluble vehicle.

One of the objects of this invention is to provide metal materials which remain perfectly free from rusting during the forming operation and are of excellent lacquerability as final product.

The second feature of this invention relates to a metal material which is produced by applying a film of oil onto the said metal material treated in accordance with the first-feature to prevent abrasion and scratches Without deteriorating adhesion of paint to the base.

The metals to be used as base or plated layer of the metal materials -of this invention include those metals on which a chromic acid treatment produces corrosion resistance, such as steel, zinc, tin, lead, chromium, aluminum, copper, magnesium, nickel, silver and alloys thereof.

The chromic acid treatment of this invention includes immersion chromate treatment, electrolytic chromate treatment and electrolytic chromic acid treatment to be conducted in aqueous solutions in which the major constituent is anhydrous chromic acid, chromate or dichromate.

The immersion chromate treatment includes irnmersion treatment of materials in an aqueous solution containing as major components one or several of the following sodium dichromate, potassium, dichromate, sodium chromate and chromic anhydride with addition of sulfuric acid, sulfates, nitric acid and fluoric compounds.

The electrolytic chromate treatment includes a cathodic electrolytic treatment of materials in an aqueous solution of chromic anhydride or sodium dichromate with or without additives such as sulfuric acid, sulfates, fluoric compounds, nitric acid manganates, tungstatcs and molybdates.

3,671,205 Patented June 20, 1972 ICC The electrolytic chromic acid treatment includes a cathodic electrolytic treatment and a chromium plating of steel in an aqueous solution of chromic anhydride with additives such as phosphoric acid, sulfuric acid, boric acid, sulfonic acid, acetic acid, chloric acid, bromic acid, fiuoric acid and their salts and fluoric compounds.

The :film obtained by the chromic acid treatment is generally considered to be in a form of hydrate oxides (xCr2O3'yCrO3-xH2O) containing trivalent chromium and hexavalent chromium, but the film obtained by the electrolytic chromic acid treatment of steel is considered to be composed of an upper layer of trivalent hydrated chromium oxide and a lower layer of metallic chromium.

The hydrated chromium oxide film formed on the metal lbase or on a metal coated thereon is corrosion resistant but is exceedingly chemically active so that organic substances especially oily substances coming into contact with the coating film immediately after the film formation are strongly adsorbed to the film.

Therefore, materials covered with the hydrated chromium oxide film have strong adhesion toward the applied organic coatings immediately after the fhn formation, but if an oily substance is absorbed in a subsequent process after the film formation the characteristics of the surface will be changed so that the adhesive property especially toward a melamine alkyd coating is reduced. Moreover, the adsorbed layer is difficult to remove by the conventional degreasing so that poor adhesion of the coating remains even after the process of degreasing.

To overcome this difliculty caused by the high adsorbing property of hydrated chromium oxide film, a substance which is compatible with paints and does not interfere with lacquer adhesion should be absorbed immediately after the formation of the film so as to prevent strong adsorption of other substances which cause poor adhesion in subsequent processes. In view of this, a metal product has been proposed (Japanese patent publication Sho 42/26,458) of which the hydrated chromium oxide film is treated with oils of allyl esters or allyl ethers. In this method, however, since a drying process is required prior to application of the above oily substances, it is a disadvantage that organic substances or dust contained in the drying air may be adsorbed to alter the surface property in the drying process so that the advantage of applied allyl compounds might be reduced. When the allyl compounds are applied by an electrostatic or a spraying method, the highly reactive unsaturated bond of allyl compounds may cause polymerization by air oxidation to raise the viscosity, resulting in incomplete atomization of the compounds and further blocking of the nozzle. On the other hand, however, application of the allyl compounds by the emulsion method is subject to unfavorable inuence due to the adsorption of surfactants and other additives. Furthermore, application of an organic solvent is also disadvantageous on account of the danger of infiammation and explosion and of the hazard to human health.

The characteristic required of the substances to be adsorbed on the hydrated chromium oxide film to prevent strong adsorption of other substances in the subsequent processes are not only that they should not interfere with the lacquer adhesion and that they themselves polymerize into the lacquer film, but also that they should be water soluble substances so that they can be adsorbed uniformly while the hydrated chromium oxide film formed is still wet after washing with Water and is free from other contaminations. These substances are also required to become substantially insoluble after an ordinary drying process, they should not be affected by in, the present invention, 'afilmof which3`,hy.dr ated l chromium oxide is the major component is formed on the surface of the metallic materials, washed with Water, dipped for a short time-in a diluteaqueous 'solution-of the water soluble vehicle, or the salme solution is sprayed on the surfaces, While the 'Surface film is'still wet, and I finally the materials aresqueezedwith rollers to make a thin uniform layer of the watersoluble vehicleon the hydrated chromium oxide iilm.

The invention will be more fully explained with reference to the accompanying drawing, in which FIGS. l to 4 illustrate several embodiments of metal pieces with coatings according to the invention.

FIG. 1 shows the cross-section of a metal material of this invention; FIG. 2 show the cross-section of a metal material of this invention when the metal base is covered by a plated layer; FIG. 3 shows the cross-section in which an oil film is applied to the metal material shown in FIG. 1; and FIG. 4 shows the cross-section in which an oil film is applied to the metal material in FIG. 2.

Referring now to FIG. l, 1 is a metal base, 2 is a hydrated chromium oxide film, 3 is a thin layer of a water soluble vehicle, FIG. 2 shows in 4 an intermediate layer of coated metal between the metal base 1 and the film 2. FIG. 3 illustrates an embodiment in which an oil film 5 is applied as a top coating to the material shown in FIG. l, and FIG. 9 is a similar showing for a modificaion of material according to FIG. 2.

The Water soluble vehicles of this invention, which are resins capable of yielding Water soluble paints by themselves, are compatible With the paint applied to the metal materials and polymerize into a coating film proper after lacquering; as a result adhesion of the paint applied is improved. In addition, the thin layer of Water soluble vehicle formed on the surface of the film of hydrated chromium oxide not only strongly adheres, but also becomes practically insoluble after the drying, and is by no means affected by such oily substances as lubricants applied to it, and thus degreasing is possible with ease without interfering with the adhesion of the organic coating.

The water soluble vehicles of this invention are classified into 5 groups as shown below.

(1) Oleoresinous water soluble vehicles Resins prepared by mixing rosin, ester gum, alkyl, phenol resin, coumarone resin, cyclopentadiene resin, petroleum resin, cashew nut shell oil, or epoxy resin to anhydrous castor oil, tung oil, linseed oil or soybean oil, and by then reacting with maleic acid; and resins prepared by replacing maleic acid by fumaric, itaconic, acrylic or citraconic acid.

(2) Water soluble alkyd resin vehicles Polyesters prepared from polyalcohols, such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitol, diglycerol, dipentaerythritol, epichlorohydrin, allylglycidylether, phenylglycidylether and epoxy resins, and dibasic acids, such as phthalic, maleic, furmaric, succinic, adipic, itaconic and citraconic acids; polyesters prepared by employing instead of above dibasic acids polybasic acids, such as benzenetricarboxylic acid, benzenetetracarboxylic acid, phosphoric acid, additives of rosin and maleic acid anhydride and maleic oils; and polyesters having polyoxymethylene bondings prepyleneglycol;

:Wateri soluble alkydr'esins' "modied byfa resolv of Vwhich the ravvfjmaterial'"isV 'cresoll ol" x'ylenol orA butyl. phenoh'fvvater' solublefalkyd "resins modified byaf-penta- -e'r'ylthritol-f ester 'ofdiplienoliacim v'and Water -soluble alkyd resins modified by a water soluble Vresin-which s-producec'lfffrori novolak by-"i'ntroduci'ng carboxyl and then methylol groups 9 i n' Waterjsoluble vehicles w Watersoluble alkyd yresi-nsIrfriodifiedby methoxymethylmelaninesg 'l such as Tv vdimetloxyrnethyltrimethylolmelamine/and hexar'nethoxymethylmelamine; vvv'a't'r -soluble 'alkyd resins lmodified by lpartiallytetheriied polymethyl- Volmefl'ainine or lpolym'ethylolurea; and" Water soluble alkyd resins modified by polymethylolmelamine, alkylenepolyamines, hyldroxypolyamines and guanidine.

(5) Water soluble acrylic resin vehicles Copolymers of acrylic or methacrylic acid with methyl acrylate, ethyl acrylate or methyl crotonate; copolymers of alkyl esters of acrylic or methacrylic acid with vinyltoluene; and hydroxymethylated copolymers of acrylamide or methacrylamide with N-vinyllactam; and copolymers of N-methylolamides with ethyl acrylate.

The water soluble vehicles shown above from (l) through (5) may be used either singly or in combination of more than two.

In case the water soluble vehicle is used singly, some paints may give only poor adhesion due to low aflinity of the applied vehicle with the base resin of the paints. To prevent this it is more desirable to use two or more water soluble vehicles in combination, and good adhesion with all kinds of paints is obtained by the alkyl resin vehicles in which epoxy resin is used as polyalcohol.

The adsorbed quantity can be arbitrarily varied by controlling the vehicle concentration in the aqueous solution. The preferred concentration, however, is 0.1 to 48% by Weight, or 3 to 100 mg./m.2 in the adsorbed quantity of vehicle. These quantities are remarkably small in comparison with those conventionally adopted for water soluble paints, for example 10 to 20% by Weight in the concentration of vehicle and 50 to 500 mg./dm..2. The application of vehicles in the present invention is not for the purpose of undercoating nor as primer in the conventional lacquering. That is to say, the applied quantity of vehicles, 3 to 100 mg./m.2, is suicient to form a thin layer of the vehicles, and baking is not required, but mere removal of water by ordinary drying methods is sufficient. In addition, the layer is extremely thin, or less than 0.1M, so that it is colorless and transparent without affecting the appearance. It does not act as a coating lilm but exhibits only a sealing effect toward adsorption of oily substances.

The lower limit of the adsorbed vehicle, 3 m.g./m.2, is considered the minimum quantity necessary to completely cover the whole surface. With vehicle below this quantity, a desirable effect cannot -be expected. The adsorbed quantity 3 mg./m.2 of the water soluble vehicle corresponds to a concentration of 0.1% by weight in a solution. Below this concentration, lacquer adhesion is not sufficient when a lubricant, for example, is applied to a metal material. On the other hand, the adsorbed quantity of vehicle above the upper limit Ing/m.2 makes the vehicle layer so thick that non-uniform squeezing with rollers may often result which is unfavorable for good appearance. The absorbed quantity 100 mg./m.2 of the water soluble vehicle corresponds to a concentration of 8% by weight in a solution. A solution of higher concentration, hence increased quantity absorbed, does not enhance the desired eiTect, but degrades the appearance and is liable to cause incomplete drying. For these reasons, the amount of the water soluble vehicle should be limited to 3 to 100 mg./m.2.

The metal materials of this invention are suited to bending or drawing, for example, where lubricants are applied during the processing and they are degreased afterward and the materials are coated with paint. More particularly, the thin layer of the vehicle strongly adheres to the hydrated chromium oxide layer, and the vehicle layer is practically insoluble and in addition does not adsorb lubricants, so that the degreasing can be conducted completely. Actually the vehicle layer is compatible with ordinary baking paints such as, for example, alkyl, melamine-alkyd, epoxy, epoxymelaminealkyd, acryl and vinyl paints. This is due to the property of the vehicle layer to polymerize into the applied organic coatings and to increase the adhesive strength of the coating layer.

The thin layer of vehicle on the metal materials of this invention is practically insoluble and can never be removed by the ordinary solvent degreasing process such as trichlene degreasing and by the emulsion degreasing, -but is partly removed from the surface when treated with a powerful alkaline degreasing agent containing sodium hydroxide or sodium silicate. In this case, however, along with the complete removal of greases, a part of the vehicle still remains on the metal surface and further improves the adhesion of paints.

Even if an oily substance is applied in the amount about 3 to l0 mg./m.2 to prevent abrasions and scratches on a metal material of this invention, direct lacquering on it is possible without any further treatment to obtain good lacquer adhesion. This may be due to the fact that the oily substance is not adsorbed on the thin layer of the vehicle, but diffuses in the paint without leaving a bad eect.

The oils to be used in this invention include D.O.S. (di- 2-ethyl-hexylsebacate), cotton seed oil, linseed oil and others.

The present invention will be better understood from theV following examples.

EXAM-PLE l In an aqueous solution containing 60 `g./l. of' chromic anhydride and 0.55 g./1. of sulfuric acid, a cold rolled steel sheet was treated electrolytically as cathode to form on the steel sheet a duplicate layer of hydrated chromium oxide and metallic chromium, washed with water, and immediately dipped for 2 seconds into a 4% aqueous solution by weight of a water soluble oleoresinous vehicle which 'was obtained by heating a mixture consisting of 75 parts of anhydrous castor oil, 5 parts of an epoxy resin (Epikote #812) and 20 parts of maleic acid anhydride, squeezed with rollers to control the adsorbed amount of the vehicle to 30 mg./m.2 and then dried at room temperature. To this sample, #60 spindle oil was applied in an amount o f 2 g./m.2, degreasing was conducted for 2 minutes with trichlene vapor, and a melamine-alkyd white coating was applied 25p. thickness -by baking. The cross-cut Erichsen test of the coating resulted in 100 in number of peeled squares.V On the other hand, however, an identical steel sheet similarly treated but with no vehicle applied adsorbs spindle oil on its surface. The cross-cut Erichsen test of the latter sample resulted in 97/ 100 in number of peeled squares.

EXAMPLE 2 A cold rolled steel sheet was treated, as in Example 1, electrolytically in chromic acid solution, Washed with water, then immediately a 0.5% aqueous solution by Weight of a water soluble alkyd resin vehicle, which was obtained by heating a mixture consisting of 40 partsof anhydrous castor oil, parts of trimethylolpropane, and 45 parts of phthalic acid, was sprayed on for 2 seconds, and then the sheet was squeezed with rollers to control the adsorbed amount of the vehicle to 10 mg./m.2, the material vwas then dried at 50 C. with hot air, and finally cotton seed oil was applied electrostatically in an amount of 8 mg./m.2. After the lapse of a month, an alkyd coating (hammer finish) was applied by baking to 25u thickness. The cross-cut Erichsen test resulted in 0/ 100 in number. of peeled squares, while the same test of a sample, to which no vehicle was applied, resulted in 100/100 in number of peeled squares.

EXAMPLE 3 After the lapse of a month, the samples in Example 2 were pressed, `using press oil #620 in a drawing ratio of 2.0, into a cylinder of 40 mm. diameter with a at bottom. After a week, these samples were degreased by dipping in cold trichlene for a minute and then by exposing to trichlene vapor for 2 minutes. A melamine-alkyd paint was applied to 30p. thickness by baking. The cross-cut test on the bottom and the side wall of the cylinder made from the sample to which the resin vehicle was applied resulted in 0/ 100 in number of peeled squares, While the same test on the cylinder made from the sample to which no vehicle was applied resulted in 96/ 100 for the bottom and 50/ 100 for the side wall.

EXAMPLE 4 An electroytic tin plate was electrolytically treated as cathode in a 3% solution of sodium dichromate to form thereon a hydrated chromium oxide film, washed with water and immediately dipped for a second in a 0.2% aqueous solution of the vehicle consisting of parts of water soluble alkyd vehicle and 20 parts of hexamethoxymethylmelamine, the former being obtained by heating a mixture consisting of 60 parts of linseed oil, 10 parts of glycerine and 30 parts of maleic acid. The wet plate was squeezed with rollers to control the adsorbed amount of the vehicle to 5 mg./m.2, dried at room temperature, and D.O.S. (di-2-ethylhexylsebacate) was applied in an amount of 5 mg./m.2 using mineral spirit as solvent.

A melamine-alkyd white coating was baked on this sample to 10u thickness and the product was pressed in a drawing ratio of 2.0 into a cylinder of the diameter 40 mm. with a at bottom. The cross-cut test on the bottom and the side wall of the cylinder resulted in 0/ 100 and l/ 100, respectively, in number of peeled squares, while the same test of the cylinder made from a sample to which no vehicle was applied was 43/ 100 and 82/ 100, respectively.

EXAMPLE 5 A cold roller steel sheet was plated with a 0.0lu layer of chromium, treated electrolytically in an aqueous solution containing 30 g./l. of chromic anhydride and 0.1 g./l. of chromium sulfate to `form thereon, a double layer of metallic chromium hydrated chromium oxide and washed .with water. Immediately thereafter, an aqueous solution was sprayed onto the coated sheet, containing 6% by weight of vehicle which consisted of 40 parts of partially butoxylated methylolurea and 60 parts of the water soluble alkyd resin employed in Example 2, then the sheet was squeezed with rollers to control the adsorbed amount of the vehicle to 70 mg./m.2, dried by blowing hot air at 60 C., cotton seed oil was applied electrostatically in an amount of 3 mg./m.2 and then Valvoline 861Q (trade name, rust preventive oils, available from Daikyo Petroleum Co. of Japan) in an amount of 5 g./m.2. After three months the sample was pressed in a drawing ratio of 2.0 into a cylinder of 40 mm. diameter with a at bottom. This was treated by spray degreasing at 60 C. for 2 seconds with a 3% solution of Parco Cleaner #358, supplied by Nihon Parkerizing Co., Ltd. and melamine alkyd coating (clear) was baked to 30u thickness. The cross-cut test was conducted on the bottom and the side wall of the cylinder, resulting in 0/ 100 in number of peeled square. On the other hand, the same treatment of an identical sample, except that a vehicle was not applied,

resulted in incomplete degreasing so that the peeled squares were 100/100 and 93/100, respectively. Furthermore, the salt spray test of the sample (without organic coating) conducted at 35 C. for 20 hours immediately after application of cotton seed oil did not produce rust at all, while the same test produced rust by 2.5% in the rusting ratio with a similar sample to which no vehicle was applied.

EXAMPLE 6 v A zinc plated steel sheet was treated by the electrolytic chromate process in an aqueous solution containing 30 g./l. of chromatic anhydride and 0.2 g./l. of sulfuric acid to form on it a lm composed mainly of hydrated chrominium oxide. Immediately after washing with water, a 1% aqueous solution of Resydrol P411, an alkyd resin modified by phenolic resin, was sprayed on, and sheet was squeezed With rollers, to control the adsorbed amount of vehicle to 15 mg./m.2, the sheet was then dried. To this surface, machine oil #120 was applied in an amount of 5 g./m.2.`After 3 months degreasing was conducted for 1 minute by dipping in cold trichlene and then for another minute with trichlene vapor, and a melamine-alkyd resin coating was baked to 25p. thickness. The cross-cut Erichen test on the above product showed /100 in number of peeled squares, while a similar sample to which no vehicle was applied proved to be 38/100.

EXAMPLE 7 A cold rolled steel sheet was first plated with chromium to 0.025# thickness, and then treated by the electrolytic chromate process in a solution containing 60 g./l. of chromic anhydride, g./l. of acetic acid and 0.5 g./l. of sodium fluorosilicate to form a lm composed mainly of hydrated chromium oxide. Immediately after washing with water, the sheet was dipped for l second into an aqueous solution containing 1% by Weight of water soluble acrylic resin vehicle consisting of a copolymer of N-methylolamide and ethyl acrylate. The sheet was then squeezed with rollers to control the adsorbed amount of the vehicle to mg./m.2, and then dried at room temperature. This sample was pressed, with #640 press oil, into a cylindrical vessel of 80 mm. diameter and 60 mm. depth, which was degreased for 1 minute by dipping in cold trichlene and for another minute with alkali (NaOH 2%, 60 C.), and then a phthalic acid alkyd coating was baked to 15p thickness. The cross-cut Erichsen test of the bottom and the side wall of the cylinder revealed to be 0/ 100 in number of peeled squares, while the same test of a cylinder made from a similar sample to which no vehicle was applied proved to be 100/100 for the bottom and 97/100, `for the side wall.

EXAMPLE 8 A cold rolled steel sheet was subjected to an electrolytic chromic acid treatment in an aqueous solution containing 50 g./l. of chromic anhydride, 0.2 g./l. of sulfuric acid and 0.4 g./l. of sodium fluorosilicate to form a double layer of hydrated chromium oxide and metallic chromium. Immediately after washing Withwater, the sheet was dipped for 1 minute in an 1.0% by weight aqueous solution of the vehicle which wasva mixture consisting of 50 parts ot the water soluble oleoresinous vehicle employed in Example 1 and 50 parts of the water soluble alkyd resin vehicle used in Example 2, squeezed with rollers to control the adsorbed amount of the vehicle to 15 mg./rn.2, and then dried at room temperature. Melamine-alkyd white coating was baked on the sheet to p thickness. The cross-cut Erichsen test of the coating film proved to be 0/100 in number of peeled squares. The above sample was further coated with Noxrust 530F, rust preventive oil, supplied by Daubert Chemical Co., Ltd. inV an amount of 5 g./m.2 and kept for 3 months. After the period, the sample was degreased-by dipping for l minute in cold trichlene and then with trichlene 8 vapor for 2 minutes, and a melamine-alkyd white coating was baked to 25p thickness.'The cross-cut Erichsen test of the coating lm resulted in 0/100 in number of peeled squares.

The cross-cut Erichsen test of a similar sample to which no vehicle was applied proved to be 23/100 in number of peeled squares when the same white coating Was applied directly, but /100 when the above Noxrust 5,30F was applied and kept for 3 months before testing.

EXAMPLE 9 A cold rolled steel sheet was plated with chromium to 0.025,1. thickness and subjected to an electrolytic chromate treatment in an aqueous solution containing 8O g./l. of sodium dichromate and 2 g./l of ammonium sulfate to form a hydrated chromium oxide lm. Immediately after washing with water, the sheet was dipped for 1 second in a 4% by weight aqueous solution of the vehicle consisting of 70 parts of the`water soluble alkyd resin vehicle employed in Example 2 and 30 parts of the water soluble acrylic resin vehicle employed in Example 7, squeezed with rollers to control the adsorbed amount of the vehicle to 45 mg./m.2, dried at 60 C., and then D.O.S. (di 2 ethylhexylsebacate) was applied in an amount of 5 mg./m.2. On two of these samples thus prepared, alkyd white coating and acrylic white coating were baked respectively to 30p. thickness, and the crosscut Erichsen test of the coating film of these samples proved to be 0/100 in number of peeled squares.

Another two samples to which the vehicle and D.O.S. were applied were pressed at a drawing ratio of 2.0 with machine oil into a cylinder of 40 mm. diameter having a hat bottom, degreased by dipping for 1 minute in cold trichlene and then for 2 minutes with trichlene vapor. Subsequently an alkyd white coating and an acrylic white coating were baked respectively to 30p thickness. The cross-cut test of these samples showed no peeling of coating both for the bottom and the side Wall.

On the other hand, however, similar samples to which no vehicle was applied but D.O.S. was applied directly and to which alkyd White coating or acryl white coating was applied, showed 97/100 or 8/100 respectively in the cross-cut Erichsen test in number of peeled squares. Further similar samples to which no vehicle was applied, but D.O.S. was applied directly were pressed into a cylinder having a flat bottom, degreased and coated. The cross-cut test of these samples showed 83/100 for the bottom and 45/100 `for the side wall of the cylinder in number of peeled squares in case of alkyd white coating 17/100 and 10/100 respectively, in case of acrylic white coating. e

EXAMPLE 10 A cold rolled steel sheet was chromium plated in an aqueous solution containing g./l. of chromic anhydride and 1.5 g./l. of sulfuric acid to form a metallic chromium layer of 0.32 g./m.2 on the sheet andl a hyldrated chromium oxide iilm of 8 mg. Cr./m.2 on the metallic chromium layer. Immediately after washing with water, the sheet was sprayed with an 1% aqueous solution of water soluble vehicle composed of 5 parts of half ester of epoxy resin (Epicote #812) and trimellitic acid anhydride, and 1 part of polymethylolmelamine (Smitexresine MW), squeezed with rollers to control the What is claimed is:

1. Metal materials receptive to organic coatings and having a film composed mainly of hydrated chromium oxide on the surface of metal or plated metal, and a layer of a water soluble vehicle containing at least .a member selected from the group consisting of oleoresinous resins, alkyd resins, aminoalkyd resins, phenolalkyd resins and acrylic resins on the hydrated chromium oxide iilm.

2. Metal materials according to claim 1 in which the water soluble alkyd resins are prepared from epoxy resins as half-esters with dibasic acids and polybasic acids.

3. Metal materials according to claim 1 in which the layer of the water soluble vehicle is in an amount of 3- 100 mg./m.2.

4. Metal materials receptive to organic coatings and having a film composed mainly of hydrated chromium oxide on the surface of metal or plated metal and a layer of a water soluble vehicle containing at least a member selected from the group consisting of oleoresinous resins, alkyd resins, aminoalkyd resins, phenolalkyd resins, and acrylic resins on the hydrated chromium oxide lm, and -a film of oil on the water soluble vehicle layer.

5. Metal materials according to claim 4 in which the layer of a water soluble vehicle is in an amount of 3-100 mg./m.2.

6. Metal materials according to claim 4 in which the oil is a member selected from the group consisting of D.O.S., cotton seed oil and linseed oil.

7. Metal materials according to claim 2 in which the plated metal has a double layer of metallic chromium and hydrated chromium oxide.

8. A metal sheet or coil receptive to organic coatings and comprising:

(a) a metallic substratum;

(b) a chromium-containing layer on said substratum, said chromium-containing layer comprising hydrated chromium oxide; and

(c) a protective, water-soluble film on said chromiumcontaining layer, said film being formed from at least one member of the group consisting of oleoresinous resins, alkyd resins, aminoalkyd resins, phenolalkyd resins and acrylic resins.

9. In a metal article, wherein a metallic substratum is coated with a chromium layer containing hydrated chromium oxide and the chromium layer is in turn coated with a corrosion resistance improving organic coating, the improvement which comprises that a water-soluble lilm, re-

10 ceptive to said organic coating, is provided between said organic coating and said chromium layer, said watersoluble lm essentially consisting of at least one member of the group consisting of oleoresinous resins, alkyd resins, aminoalkyd resins, phenolalkyd resins and acrylic resins.

10. In a method of coating metallic articles with an organic coating, wherein a metallic substratum having a surface layer comprising hydrated chromium oxide is coated with the organic coating, the improvement which comprises that, prior to applying said organic coating, said surface layer is treated vn'th an aqueous solution containing at least one member selected from the group consisting of oleoresinous resins, alkyd resins, aminoalkyd resins, phenolalkyd resins and acrylic resins, whereby a water-soluble film receptive to said organic coating is formed on said surface layer.

11. The improvement of claim 10, wherein, after the formation of said water-soluble film and prior to the application of said organic coating, lubricating oil is applied to said metallic article, the metallic article is formed into a desired shape and degreased, whereafter said organic coating is applied.

12. A method of forming a metal sheet into a metal object which comprises:

(a) applying an aqueous solution of at least one member of the group consisting of oleoresinous resins, alkyd resins, aminoalkyd resins, phenolalkyd resins and acrylic resins to a metal sheet having a surface layer containing hydrated chromium oxide and drying the sheet, whereby a water-soluble film is formed on said surface layer;

(b) applying lubricating oil to said sheet;

(c) forming the sheet into a desired object;

(d) degreasing the object; and

(e) applying an organic coating on said water-soluble film.

References Cited UNITED STATES PATENTS 3,526,486 9/1970 Smith et al. 29-183.5 3,479,162 ll/ 1969 Yanabu et al. 29-195 L. DEWAYNE RUTLEDGE, Primary Examiner .E. L. WEISE, Assistant Examiner U.S. C1. X.R. 117-49, 69 

